What is “small hydropower”
- In the U.S., “small hydro” typically refers to hydropower plants with generating capacity on the order of up to ~10 MW (some definitions go up to 30 MW depending on regulatory context).
- These small-scale plants often make use of existing dams, canals, pipelines, or irrigation infrastructure rather than building large new dams, which helps reduce environmental impacts and costs.
- Types include run-of-river (diverting part of a stream without huge reservoirs), low-head canal or conduit hydro, retrofits of old dams or water-management facilities, and similar low-impact installations.
How common is small hydro is in the U.S.
- According to a report from Oak Ridge National Laboratory (ORNL), small hydro plants (≤ 10 MW) make up about 75% of the U.S. hydropower fleet by number of plants.
- Despite being numerous, these small hydro plants contribute a relatively small share of total hydropower capacity — large hydro accounts for the majority of overall generation capacity.
- Historically, assessments estimate that many more small-hydro / low-power sites remain untapped: there are thousands of technically feasible small hydro / micro-hydro locations across streams, canals, non-powered dams and water conduits that could be developed.
- Because small hydro can be built using existing water infrastructure or modest new works, it is often viewed as a low-cost, low-impact route to adding renewable energy, especially in rural or distributed settings.
Examples of U.S. Small Hydropower Projects
- Koma Kulshan Project — a run-of-the-river hydroelectric facility in Washington State. Its capacity is about 13.3 MW, and it sits on tributaries of a natural lake (i.e. minimal large-dam reservoir).
- Bowersock Mills & Power Company — a small hydro facility on the Kansas River, generating about 2.35 MW annually (with expansion underway to increase output).
- Retrofits and canal/irrigation-based small hydro — many small hydro installations in the U.S. repurpose irrigation canals, water-treatment outfalls, or old dams, because such infrastructure can often be adapted to electricity generation with modest impact.
Why Small Hydro Matters & What Limits It
Why it matters:
- It offers distributed, low-impact renewable energy — useful especially for rural or remote areas, small towns, or regions not suited to large dams or big hydropower plants.
- It can make use of existing water infrastructure, reducing costs and environmental impact.
- It diversifies the energy grid, providing clean power that — in many settings — can be more stable than intermittent renewables like solar or wind.
Challenges / limitations:
- Much of the easiest large-scale hydro potential is already used in the U.S. What remains is often small-scale, low-head or low-flow sites.
- Economic viability sometimes remains marginal — retrofits or small projects may struggle to be profitable unless aided by incentives, favorable regulation and efficient permitting.
- Small hydro collectively contributes less to total hydropower output compared to large plants; scaling up requires many small installations rather than a few big ones.